I was just reading an article in the new issue of Discover. The gist of it is that a number of observations of astronomical bodies indicate that there is more matter there than can be accounted for, Dark Matter. The article suggested that rather than propses this new, unknown entity, we should apply Occam's Razor (Do not multiply entities yada yada yada...) and re-evaluate our theories on gravity and Newtonian physics.

Flogiston, by the way, was believed to be the invisible matter in combustibles that had negative mass. Early experiments revealed that the products of combustion had more mass than the combustible material. Flogiston was what they came up with to explain it. They had failed to consider the added mass of the oxygen consumed in the combustion process. Now there a few radicals suggesting that Dark Matter falls into the same category.

This would not be the first time Newton was refuted. His laws of optics stated that the refractory index of all materials was proportional for all wavelengths. Therefore, an achromatic lens was not possible. It was taken as cannon, and no one even attempted to make an achromatic lens for almost 200 years.

Has anyone else read this article? Hopefully someone who knows more about physics than I do.

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To apply Occam's Razor means to prefer the simplest, most straightforward explanation with the fewest assumptions. I don't see how revising the laws of gravity (which seem to have worked exquisitely for the past 300+ years) fits in with Occam's concept.

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One of the early applications of Sir William of Occam's razor was to refute the use of epicycles to explain odd movements of the planets in a earth centered universe. It was not easy changing peoples mind, but the solution was more simple, and, as it turns out, correct.

The argument is that we are basing our understanding of gravity based on how it acts here on Earh on objects weighing at most a few tons, over the distance of maybe a few thousand miles. We are then applying the same figures to objects like galaxies, over distances of megaparsecs. What is being proposed is that maybe our understanding of gravity can not be applied on that scale.

another possibility is that there is something wrong with our observations. And then there is the possibiliy that dark matter really does exist.

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That which cannot be remedied must be endured.

Actually we are basing our understanding of gravity based on how it acts in our Solar System on objects weighing at most 2 octillion (yes, octillion!) tons over distances of a few billion kilometers. This still does not detract from the possibility that gravity might not scale up to galaxies and clusters of galaxies, I just want readers to know that the behavior of gravity is known over a wider range of magnitudes than you suggested. Oh, and also some question whether gravity behaves the same at submillimeter scales.

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The bar has been lowered for the promotion of ATM ideas; the bar for the acceptance of ATM ideas must remain high.

Good point. I was not thinking about the planets. I am also not sure what we know about he movements of stars in our local area, like the way binary stars move relative to each other. One other thing though. the probes we have had leave the solar system are slowing down faster than they should. This would seem to suggest that there are vast ammounts of dark matter here in our own solar system. So finding it should not be that hard if it is here.

I am going to read that article again. I really do not know enough about this.

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That which cannot be remedied must be endured.

I'm not so sure about this. Isn't this still quite controversial?

Well, there might be simpler explanations.

As to your initial question, the major gravity revision proposed is Modified Newtonian Dynamics (or MOND), which I thought was pretty well dead, but perhaps its demise was exaggerated.

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Everyone is entitled to his own opinion, but not his own facts.

Also, if there were vast amounts of dark matter here in our own solar system, it would affect the planetary orbits, but such an effect is not observed.

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Everyone is entitled to his own opinion, but not his own facts.

So, you think the most likely explanation is that our measurements are wrong? Perhaps. I know it is controversial, that is what makes it worth discussing. To the best of my knowledge there is no evidence of dark matter in out solar syslem. But why not? I suppose since it occupies the vast intergalactic space if can be very sparse, but still have a vast total mass, but I believe it is also supposed to occupy pace within the galaxies as well. So is it distributed in such a way as to be significant on the galactic and intergalactic scale, but undetectable on the stellar scale? I suppose that if all matter in the universe were evenly dispersed it would be so sparse that you would not be able to detect it.

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That which cannot be remedied must be endured.

It doesn't have to be an error in measurement. The rate of slowing is pretty small (about the photon pressure of a 60 watt light bulb), and could be adequately explained by anisotropic radiation of waste heat from the RTG (see here). Of course, there are other possible explanations, but the point is that this effect, even if quite real, doesn't require any new physics.

Its also important to keep in mind that in spiral galaxies the rotation curve remains flat beyond the optical portion of the disk which indicates that the dark matter (if present) has to be in a halo surrounding the disk. I don't have the reference at hand, but there were a couple of studies completed with the Hipparcos data that indicate that there actually is very little dark matter in the solar neighborhood.

Ripper, you might also want to look at this thread which discusses some tentative evidence that the dark matter could potentially exist as baryonic dark matter as opposed to the non-baryonic dark matter that is currently favored. Its way too early to make a final call on this one but perhaps another decade of data will help.

Keep in mind that the hypothesis that all dark matter is baryonic is certainly not favored because it conflicts with Big Bang nucleosynthesis.

I just re-read the part of the article that dealt with the slowing down of the space probes, specifically Pioneer 10, Pioneer 11, Ulysses, and Galleleo. What was noticably absent was any mention of just how much they were slowing down. It does mention that physicists have only been able to measure gravitational force to about 5 decimal places. So how significant does this extra ammount of gravity that is slowing down our probes have to be if they can accurately measure its effect?

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That which cannot be remedied must be endured.

Dang. I can't remember right now, but there was an article about this in The Planetary Report a few issues back. Lemme see if I can find it tonight (no guarantee. Wife and I are rearranging our books and whenever we do that Things Get Lost).

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[pedant mode]
That's PHlogiston, with a PH, not an F.
[/pedant mode]

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Actually, wasn't it "phlogiston"? It was an early theory to explain heat.

http://www.infoplease.com/ce6/sci/A0838824.html